Help

I'm in need of some serious help. I used to be very outgoing and friendly. Now I'm very insecure and tend to be jealous. I don't like to go out anymore or meet new people. This is starting to become a major problem with my boyfriend because he is very outgoing and likes to go out. I can feel when it starts and I tell myself to knock it off, that I'm being silly and have no reason to worry. My boyfriend has never given me a reason to wonder and has been understanding. But its starting to become a problem. We've been together for 2 1/2 years, and I'm not getting any better. I'm getting worse. I've tried Zoloft with only begative results. What can I do?